This invention relates generally to media sheet handling systems, and more particularly to a printing mechanism that can produce images on both sides of a media sheet.
Printing to two sides of a media sheet, referred to as duplex printing, is a desirable feature in a printing system. The advantages of duplex printing include reducing the amount of paper required in one-sided (simplex) printing, and generating print sets with layouts resembling that of professionally printed books. Conventional duplex printing devices, as exemplified by what is disclosed in U.S. Pat. No. 5,392,092 for "Printing Device Duplexing Mechanism and Method Therefor," flip the media sheet over with respect to its original position and swap the leading edge for the trailing edge in printing a second side of the media sheet. Since the page is now positioned with what was originally the trailing edge as the leading edge, as the second side of the media sheet is printed, the image has to be written in a bottom-to-top and right-to-left manner. Thus the formatter of the printer has to correspondingly reverse the order of the data supplied to the print engine.
In inkjet printers, drying of media sheet brings another major challenge for duplex printing, because a printed side of a media sheet tends to wrap around the drive roller surface when the second side is printed. U.S. Pat. No. 5,772,343 for "Media Handling System for Duplex Printing," provides one solution to duplex printing for such printers. In this solution, the media sheet, after its first side is printed and before it is fed back for printing its second side, has to be held in the air space of the printer output region for a predetermined time period for the wet ink to dry. Since the printer is waiting idly for the drying, printing efficiency therefore is unnecessarily degraded.
Accordingly, there is a need for a convenient and efficient way to realize duplex printing.